The following sections provide the approved standard infiltration testing specifications.

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1 APPENDIX F.2 INFILTRATION TESTING To properly size and locate stormwater management facilities, it is necessary to characterize the soil infiltration conditions at the location of the proposed facility. All projects that propose onsite infiltration must evaluate existing site conditions and determine: 1. If the infiltration rate is adequate to support the proposed stormwater management facility (satisfied through the Simplified Approach infiltration test). or 2. The design infiltration rate prior to facility design (satisfied through Presumptive or Performance infiltration testing conducted by a qualified professional). The following sections provide the approved standard infiltration testing specifications. Simplified Approach Open Pit Infiltration Test The purpose of the Simplified Approach is to provide a method which can be conducted by a nonprofessional for design of simple stormwater systems on small projects. The Simplified Approach open pit test is applicable only to projects on private property with less than 10,000 square feet of new or redeveloped impervious area (see Section 2.2.1). The results of infiltration testing must be documented on the Simplified Approach Form (see Appendix D.3). The Simplified Approach cannot be used to find a design infiltration rate. The intent of the open pit test is to determine whether or not the local infiltration rate is adequate (2 inches/hour or greater) for the predesigned stormwater facilities described in Section 2.3 (infiltration swales, basins, planters, drywells, and trenches). The Simplified Approach Infiltration Test does not need to be conducted by a licensed professional. Simplified Approach Procedure 1. A simple open pit infiltration test is required for each facility designed through the Simplified Approach. The test should be where the facility is proposed or within the immediate vicinity. 2. Excavate a test hole to the depth of the bottom of the infiltration system, or otherwise to 4 feet. The test hole can be excavated with small excavation equipment or by hand using a shovel, auger, or post hole digger. If a layer hard enough to prevent further excavation is encountered, or if noticeable moisture/water is encountered in the soil, stop and measure this depth from the surface and record it on the Simplified Approach Form. Proceed with the test at this depth. F.2-1

2 3. Fill the hole with water to a height of about 6 inches from the bottom of the hole, and record the exact time. Check the water level at regular intervals (every 1 minute for fast-draining soils to every 10 minutes for slower-draining soils) for a minimum of 1 hour or until all of the water has infiltrated. Record the distance the water has dropped from the top edge of the hole. 4. Repeat this process two more times, for a total of three rounds of testing. These tests should be performed as close together as possible to accurately portray the soil s ability to infiltrate at different levels of saturation. The third test provides the best measure of the saturated infiltration rate. 5. For each test pit required, submit all three testing results with the date, duration, drop in water height, and conversion into inches per hour. If the results of the Simplified Approach open pit test show an infiltration rate greater than 2.0 inches per hour, the applicant can proceed with Simplified Approach facility design (where applicable). If the applicant would like to use an infiltration rate for design purposes, a Presumptive or Performance Infiltration Test must be conducted. Presumptive and Performance Infiltration Testing The Presumptive Approach (Section 2.2.2) or Performance Approach (Section 2.2.3) must be used for all public and private developments where the Simplified Approach is not applicable. The qualified professional must exercise judgment in the selection of the infiltration test method. The three infiltration available testing methods used to determine a design infiltration rate are: Open pit falling head (see page F.2-4) Encased falling head (see page F.2-6) Double-ring infiltrometer (see page F.2-7) Where satisfactory data from adjacent areas is available that demonstrates infiltration testing is not necessary, the infiltration testing requirement may be waived. Waiver of the site specific testing is subject to approval by the city stormwater system design reviewer. Recommendation for foregoing infiltration testing must be submitted in a report which includes supporting data and is stamped and signed by the project geotechnical engineer or project geologist. F.2-2

3 Testing Criteria 1. Testing must be conducted or overseen by a qualified professional. This professional must be a Professional Engineer (PE) or Registered Geologist (RG) licensed in the State of Oregon. 2. The depth of the test must correspond to the facility depth. If a confining layer, or soil with a greater percentage of fines, is observed during the subsurface investigation to be within 4 feet of the bottom of the planned infiltration system, the testing should be conducted within that confining layer. Based on DEQ requirements and conformance with Appendix F.1, the boring log must be continued to a depth adequate to show separation between the bottom of the infiltration facility and the seasonal high groundwater level. (The boring depth will vary, based on facility depth.) See Appendix F.1 for further details on depth to water investigations. 3. Tests must be performed in the immediate vicinity of the proposed facility. Exceptions can be made to the test location provided the qualified professional can support that the strata are consistent from the proposed facility to the test location. 4. Infiltration testing should not be conducted in engineered or undocumented fill. Minimum Number of Required Tests Land Division A total of two infiltration tests for every 10,000 square feet of lot area available for new or redevelopment. An additional test for every 10,000 square feet of lot area available for new or redevelopment. At least one test for any potential street facility. One test for every 100 lineal feet of infiltration facility. No more than five tests are required per development (at the discretion of the qualified professional assessing the site, as well as the City of Portland). Tests performed for a proposed land division can be used at the building permit stage as long as the results of the test are submitted with the separate applications. Building Permits The Simplified Approach requires one infiltration test for every proposed facility. The Presumptive and Performance Approaches: F.2-3

4 Require at least one test for any proposed street facility. Require one test for every 100 lineal feet of proposed infiltration facility. The number of tests is at the discretion of the qualified professional assessing the site, as well as the City of Portland. Where multiple types of facilities are used, it is likely that multiple tests will be necessary, since an infiltration test can test only a single soil stratum. It is highly recommended to conduct an infiltration test at each stratum used. City staff reserve the right to require additional testing. Factors of Safety Exhibit F.2-1 lists the minimum allowable factors of safety applied to field obtained infiltration rates for use in stormwater system design. To obtain the infiltration rate used in design, divide the infiltration rate measured in the field by the factor of safety. The factor of safety used in design should be chosen by collaboration between the geotechnical engineer or geologist overseeing the infiltration testing and the civil engineer designing the stormwater management system. Determination of the factor of safety should include consideration of project specific conditions such as soil variability, testing methods, consequences of system failure, complexity of proposed construction, etc. Note that the maximum allowable design infiltration rate is 20 inches per hour. Exhibit F.2-1: Minimum Allowable Factor of Safety Test Method Minimum Required Factor of Safety Encased Falling Head 2 Open Pit Falling Head 2 Double-Ring Infiltrometer Public Facilities: 1 Private Facilities: 2 Presumptive & Performance Infiltration Testing Instructions Open Pit Falling Head Procedure The open pit falling head procedure is performed in an open excavation and therefore is a test of the combination of vertical and lateral infiltration. 1. Excavate a hole with bottom dimensions of approximately 2 feet by 2 feet into the native soil to the elevation of the proposed facility bottom. The test can be F.2-4

5 conducted in a machine-excavated pit or a hand-dug pit using a shovel, post hole digger, or hand auger. If smooth augering tools or a smooth excavation bucket is used, scratch the sides and bottom of the hole with a sharp pointed instrument, and remove the loose material from the bottom of the test hole. 2. Fill the hole with clean water a minimum of 1 foot above the soil to be tested, and maintain this depth of water for at least 4 hours (or overnight if clay soils are present) to presoak the native material. In sandy soils with little or no clay or silt, soaking is not necessary. If after filling the hole twice with 12 inches of water, the water seeps completely away in less than 10 minutes, the test can proceed immediately. 3. Determine how the water level will be accurately measured. The measurements should be made with reference to a fixed point. A lath placed in the test pit prior to filling or a sturdy beam across the top of the pit are convenient reference points. The tester and excavator should conduct all testing in accordance with OSHA regulations. 4. After the presaturation period, refill the hole with water to 12 inches above the soil and record the time. Alternative water head heights may be used for testing provided the presaturation height is adjusted accordingly and the water head height used in infiltration testing is 50 percent or less than the water head height in the proposed stormwater system during the design storm event. Measure the water level to the nearest 0.01 foot (⅛ inch) at 10-minute intervals for a total period of 1 hour (or 20-minute intervals for 2 hours in slower soils) or until all of the water has drained. In faster draining soils (sands and gravels), it may be necessary to shorten the measurement interval in order to obtain a well defined infiltration rate curve. Constant head tests may be substituted for falling head tests at the discretion of the professional overseeing the infiltration testing. 5. Repeat the test. Successive trials should be run until the percent change in measured infiltration rate between two successive trials is minimal. The trial should be discounted if the infiltration rate between successive trials increases. At least three trials must be conducted. After each trial, the water level is readjusted to the 12 inch level. Enter results into the data table (See Exhibit F.2-3). 6. The average infiltration rate over the last trial should be used to calculate the unfactored infiltration rate. Alternatively, the infiltration rate measured over the range of water head applicable to the project stormwater system design may be used at the discretion of the professional overseeing the testing. The final rate must be reported in inches per hour. See the calculation following Exhibit F.2-3. F.2-5

6 7. Upon completion of the testing, the excavation must be backfilled. 8. For very rapidly draining soils, it may not be possible to maintain a water head above the bottom of the test pit. If the infiltration rate meets or exceeds the flow of water into the test pit, conduct the test in the following manner: A. Approximate the area over which the water is infiltrating. B. Using a water meter, bucket, or other device, measure the rate of water discharging into the test pit. C. Calculate the infiltration rate by dividing the rate of discharge (cubic inches per hour) by the area over which it is infiltrating (square inches). Note that a maximum infiltration rate of 20 inches per hour can be used in stormwater system design. Encased Falling Head Test The encased falling head procedure is performed with a 6-inch casing that is embedded approximately 6 inches into the native soil. The goal of this field test is to evaluate the vertical infiltration rate through a 6-inch plug of soil, without allowing any lateral infiltration. The test is not appropriate in gravelly soils or in other soils where a good seal with the casing cannot be established. 1. Embed a solid 6-inch diameter casing into the native soil at the elevation of the proposed facility bottom (see Exhibit F.2-2). Ensure that the embedment provides a good seal around the pipe casing so that percolation will be limited to the 6-inch plug of the material within the casing. This method can also be used when testing within hollow stem augers, provided the driller and tester are reasonably certain that a good seal has been achieved between the soil and auger. 2. Fill the pipe with clean water a minimum of 1 foot above the soil to be tested, and maintain this depth for at least 4 hours (or overnight if clay soils are present) to presoak the native material. Any soil that sloughed into the hole during the soaking period should be removed. In sandy soils with little or no clay or silt, soaking is not necessary. If after filling the hole twice with 12 inches of water, the water seeps completely away in less than 10 minutes, the test can proceed immediately. 3. To conduct the first trial of the test, fill the pipe to approximately 12 inches above the soil and measure the water level to the nearest 0.01 foot (⅛ inch). Alternative water head heights may be used for testing provided the presaturation height is F.2-6

7 adjusted accordingly and the water head height used in infiltration testing is 50 percent or less than the water head height in the proposed stormwater system during the design storm event. The level should be measured with a tape or other device with reference to a fixed point. The top of the pipe is often a convenient reference point. Record the exact time. 4. Measure the water level to the nearest 0.01 foot (⅛ inch) at 10-minute intervals for a total period of 1 hour (or 20-minute intervals for 2 hours in slower soils) or until all of the water has drained. In faster draining soils (sands and gravels), it may be necessary to shorten the measurement interval in order to obtain a well defined infiltration rate curve. Constant head tests may be substituted for falling head tests at the discretion of the professional overseeing the infiltration testing. Successive trials should be run until the percent change in measured infiltration rate between two successive trials is minimal. The trial should be discounted if the infiltration rate between successive trials increases. At least three trials must be conducted. After each trial, the water level is readjusted to the 12 inch level. Enter results into the data table (see Exhibit F.2-3). 5. The average infiltration rate over the last trial should be used to calculate the unfactored infiltration rate. Alternatively, the infiltration rate measured over the range of water head applicable to the project stormwater system design may be used at the discretion of the professional overseeing the testing. The final rate must be reported in inches per hour. See the calculation following Exhibit F Upon completion of the testing, the casing should be pulled and the test pit backfilled. F.2-7

8 Exhibit F.2-2: Encased Falling Head Procedure EXISTING GROUND SURFACE EXCAVATE OR USE SOIL-BORING CASING GOOD SEAL BETWEEN SOIL AND CASING IS NECESSARY 6" DIAMETER SOLID CASING 6" PROPOSED DEPTH OF TRENCH OR FACILITY BOTTOM Double Ring Infiltrometer Test The double-ring infiltrometer test procedure should be performed in accordance with ASTM The test is performed within two concentric casings embedded and sealed to the native soils. The outer ring maintains a volume of water to diminish the potential of lateral infiltration through the center casing. The volume of water added to the center ring to maintain a static water level is used to calculate the infiltration rate. The double-ring infiltrometer is appropriate only in soils where an adequate seal can be established. F.2-8

9 Reporting Requirements The following information should be included in the Infiltration Testing Report. The Infiltration Testing Report should be attached to the project s Stormwater Management Report: 1. Statement of project understanding (proposed stormwater system). 2. Summary of subsurface conditions encountered. 3. Summary of infiltration testing including location and number of tests and testing method used. Discussion of how the tests were performed (i.e. pipe type or diameter or test pit dimensions). 4. Infiltration testing results in inches per hour. 5. Recommended design infiltration rate. 6. Groundwater observations within exploration and an estimate of the depth to seasonal high groundwater. 7. Site plan showing location of infiltration tests. 8. Boring or test pit logs. The logs should include an associated soil classification consistent with ASTM D , Standard Practice for Classification for Description and Identification of Soils (Visual-Manual Procedure). The logs should also include any additional pertinent subsurface information, such as soil moisture conditions, depth and description of undocumented or engineered fill, soil color and mottling conditions, soil stiffness or density, and approximate depth of contact between soil types. 9. Infiltration Test Data Tables (see following pages for example and blank tables) F.2-9

10 Exhibit F.2-3: Example Infiltration Test Data Table Location: Lot 105, Point Heights Subdivision Depth to bottom of hole: 57 inches Tester s Name: C.J. Tester Tester s Company: Tester Company Tester s Contact Number: Depth (feet): Date: 6/28/2008 Test Hole Number: 3 Dimension of hole: 0.5 feet diameter Soil Texture: Black Top Soil Brown SM Brown ML Brown CL Presaturation Start Time: Presaturation End Time: Time: Time interval (minutes): Measure ment, (feet): Drop in water level, (feet): Infiltration rate, (inches per hour): Test Method: Encased Falling Head Remarks: 9: Filled with 6 9: : : : : : : Adjusted to 6 level for Trial #2 Calculation is performed for each water level drop = (Drop in water level/time interval) x conversion = 0.055ft/20min x (12in/ft) x (60min/hr) = 1.98 inches per hour F.2-10

11 Location: Date: Test Hole Number: Depth to bottom of hole: Dimension of hole: Test Method: Tester s Name: Tester s Company: Tester s Contact Number: Depth (feet): Soil Texture: Presaturation Start Time: Presaturation End Time: Time: Time Interval (minutes): Measure ment, (feet): Drop in water level, (feet): Infiltration rate, (inches per hour): Remarks: F.2-11

Stormwater Standards. Clackamas County Service District No. 1. Infiltration Testing Guide

Stormwater Standards. Clackamas County Service District No. 1. Infiltration Testing Guide Stormwater Standards Clackamas County Service District No. 1 APPENDIX E Infiltration Testing Guide Table of Contents Appendix E - Infiltration Testing Guide... Page E.1 General... 1 E.2 Basic Method -